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Extension of the room-temperature operation wavelength of GaSb-based type-I laser diodes up to 3.6 mm is presented. Episide-up mounted ridge waveguide lasers with five compressively strained quantum-wells exhibit lasing in pulsed operation with a threshold current densitiy of 862 A/cm^sup 2^ at infinite resonator length at 15deg;C and 20 mW of average output power per facet.
Introduction: Long-wavelength semiconductor lasers, emitting above 2 mm, are attractive light sources for various gas sensing applications by means of tunable diode laser absorption spectroscopy (TDLAS) [1]. So far, the most promising candidates to cover the spectral region from 2 to 3 mm seem to be GaSb-based type-I lasers, where excellent laser performance has been reported by various groups [2, 3]. The development of laser sources emitting in the range of 3 to 4 mm has been facing major difficulties; however, several approaches are being investigated for this purpose, namely the interband-quantum cascade laser (ICL) [4], direct short wavelength generation in quantum-cascade lasers (QCLs) [5], second-harmonic generation with QCLs [6] and type-I GaSb based lasers [7, 8]. The latter approach is very promising because of the utilisation of type-I alignment, yielding good spatial overlap of electron-hole wave-functions and increased radiative recombination. Unfortunately, severe problems arise with increasing the emission wavelength. Non-radiative loss mechanisms, such as Auger and inter-valence band absorption increase dramatically. Moreover, the epitaxial growth of quantum-well (QW) material becomes complicated owing to in-situ annealing effects [9] which lead to a significant increase in bandgap energy during epitaxial growth and make it difficult to achieve long emission wavelengths. These challenges are well illustrated by the fact that after the first demonstration of room-temperature operation of the GaSb-based type-I laser at 3.26 mm [10] it took three years to extend the emission wavelength to 3.36 mm [7] and another two years to shiftit to 3.44 mm [8]. In this Letter, we report the extension of the room-temperature operation wavelength of type-I GaSb-based lasers up to 3.6 mm by using advanced heterostructure designs based on quinternary AlGaInAsSb alloys. This wavelength is of specific interest for methane (CH4) detection [11].
Epitaxial growth and device fabrication: Laser structures have been grown on n-GaSb substrates in a...